1. Technical Field
Several aspects of the present invention relate to a manufacturing method of a three-dimensional structure and more particularly to a manufacturing method of a three-dimensional structure in which porous sheets are laminated, and a manufacturing device suitable for practicing the manufacturing method.
2. Related Art
A three-dimensional modeling method, which is also called “rapid prototyping”, is technologies that have been developed so as to evaluate the design and confirm functions by actually manufacturing a designed structure as a three-dimensional object.
In the three-dimensional modeling method, a manufacturing approach called “layered manufacturing” is generally used in which three-dimensional CAD (computer aided design) data in a desired shape is sliced to produce thin plates and the plates are stacked, thereby manufacturing a three-dimensional structure.
Layered manufacturing is classified into stereolithography (modeling methods using a liquid resin that is cured by being irradiated with ultraviolet (UV) rays), selective laser sintering (modeling methods in which powder is spread in a layer and then is solidified by laser sintering or adding a binder), laminated object manufacturing (LOM) (modeling methods of repeating supply, bond and cut of a paper sheet), inkjet methods (modeling methods of applying a liquid material and layering the material to form a shape), extrusion methods (a nozzle edge from which a material is squirted is run in a manner of drawing a picture with a single stroke to form a layer) and the like.
Three-dimensional modeling methods in the related art are only technologies for manufacturing design samples, and therefore photocurable materials, powder materials, paper sheets or the like are mainly used in the methods.
Although metal, ceramic and other materials are used in some of the methods, the realities are that there is little discussion on the functionality of materials for three-dimensional structures.
In contrast, an approach called “rapid manufacturing” is proposed that uses three-dimensional objects manufactured directly as articles of practical use.
A concept of manufacturing three-dimensional structures by using functional materials is thus being implemented.
However, manufacturing three-dimensional structures by using various desired materials is considered to be difficult with the existing three-dimensional modeling methods.
Among three-dimensional modeling methods of the related art, methods of using a laser for formation have restriction on materials, such as using a photocurable resin or sintering fine particles of metal and ceramics by a laser.
In selective laser sintering, part of a layer formed of powder is solidified with an adhesive serving as a binder, and therefore there is also restriction that the material needs to be a mixture of powder and a binder.
LOM uses paper sheets in the current conditions and is placed as a tool for reproducing a designed three-dimensional shape.
The material for use in this method is limited to paper or some of polymer materials.
On the other hand, inkjet methods and extrusion methods are said to have possibilities of selecting the liquid material among wide-ranging, various materials.
By way of example, structures can be manufactured by using metal fine particles for forming metal three-dimensional structures and sol liquids for forming ceramics.
However, when articles of practical use are produced by using functional materials by a three-dimensional modeling method, their formation time is a very important factor.
In particular, extrusion methods generally supply materials from one nozzle, and therefore has a drawback in that it takes a very long formation time for a three-dimensional structure.
Further, extrusion methods supply materials with relatively high viscosity from the nozzle.
Therefore, the real situation is that some materials such as polymeric material and sol liquids can be formed but the scope of material selection is not so broad.
In contrast, regarding inkjet methods, the liquid materials that can be discharged are limited to ones with relatively low viscosity, but their discharge speeds are relatively fast, several KHz, and a large number of nozzles can be used for drawing.
Accordingly, inkjet methods have advantages in formation time over extrusion methods.
However, there are few inkjet materials such as UV curable resins that have low viscosity during discharge and remain as solids after being cured.
An inkjet material from which the solvent evaporates and in which the solid content is left is of the general type.
To reduce the viscosity during inkjet discharge, the solid concentration is suppressed to be low, about 10%.
The film thickness that can be formed by one drawing therefore becomes thin.
This thin film thickness results in a drawback in that the formation time of a three-dimensional structure becomes long.
Moreover, it is difficult to freely form an overhanging shape and the like because the ink has low viscosity.
As a solution to the drawbacks, a method is proposed that forms the targeted pattern of an ink material in a desired shape by simultaneously patterning, using an inkjet method, the material together with a support member that can be removed after the formation.
However, there still remain a drawback and a problem.
The drawback is that two kinds of ink, i.e., ink for forming a three-dimensional structure and ink for support member need to be applied and therefore the formation time of a structure becomes long because of replacement of ink heads.
The problem is that two kinds of ink, solvents and the like are to be selected so that mixture of the two kinds of ink is avoided and only the support member can be easily removed.
Also, during the control in a desired shape, after an inkjet droplet has been once dried and solidified, the next inkjet droplet needs to be supplied.
It is difficult to supply inkjet droplets one after another.
Thus, there is a problem that actual formation process speeds considerably decrease due to such processes of dry and solidification,
As one application of three-dimensional modeling methods, manufacturing scaffolds for artificial organs attract expectations.
Practical implementation of artificial culture of cell tissues of bones and skins has already started.
In the future, developments into practical implementation of artificial culture of organs that require more complex microstructures are anticipated.
To realize an artificial organ of heart, liver, kidney or the like, a platform (model) structure called a “scaffold” is formed of a biocompatible material, biological materials (biological factors) such as various cells and growth factors are supplied into the structure, and cells are cultured in a culture solution.
The material for a scaffold is preferably a biodegradable material.
It is preferable that the scaffold material be gradually decomposed with the growth of cell tissues and eventually all the material be replaced by the cell tissues.
To realize an artificial organ of heart, liver, kidney or the like, microstructures need to be formed in a scaffold.
First, the scaffold needs to be porous in order for cell tissues and the like to grow, and its porosity is preferably 80% or more.
It is preferable that such microstructures (micro-compartment) be formed such that the pitch is on the order of about 100 to 200 microns.
Further, microstructures having a little larger size than the above are needed.
In the case of liver as a special example, tubular structures on the order of millimeters or submillimeters for transporting bile generated in an artificial liver to the digestive system need to be spread in the organ.
As described above, to actualize a scaffold for an artificial organ, technologies are needed that can form microstructures in an arbitrary pattern and can manufacture a three-dimensional structure in an arbitrary shape by using a material being porous and biodegradable.
Not rapid prototyping that copies only a three-dimensional shape but three-dimensional structure manufacturing that also has vital functions on a high level, that is, rapid manufacturing technologies are desired to be realized.
Further, preferably, technical developments are expected to realize manufacturing of a scaffold being a model of an artificial organ for a relatively short time.